The present invention relates generally to semiconductor device manufacturing processes and, more particularly, to an ammonia-peroxide wastewater treatment system for treating wastewater produced in semiconductor device manufacturing.
In addition to environmental pollution, industrial water consumption is being closely monitored by regulatory agencies that are demanding water consumption be reduced and that discharged wastewater have low levels of solids and contaminants. The semiconductor manufacturing industry not only consumes an ever-increasing amount of water but, as a consequence, also ends up discharging large volumes of wastewater. For example, a chemical mechanical polishing (CMP) involves a polishing slurry composed of an oxidant such as hydrogen peroxide (H2O2), an abrasive, complexing agents, and other additives. The polishing slurry is used with a polishing pad to remove excess copper from a wafer. Ammonia (NH3) is another process chemical that is used in semiconductor device manufacturing. Ammonia may be used, for example, in the deposition of silicon nitride and other nitride materials. Further, ammonia combined with aqueous hydrogen peroxide is used in various semiconductor cleaning operations.
One existing process for removing high concentrations of peroxide and ammonia from semiconductor wastewater involves chemically treating the peroxide on an industrial scale, optionally followed by nitrification and denitrification of the ammonia through biological treatment processes. Specifically, peroxide laden wastewater is chemically treated by adding large quantities of sodium bisulfite (NaHSO3), used as a reducing agent, and large quantities of sodium hydroxide (NaOH), a caustic used to neutralize the acidity of the sodium bisulfite. More specifically, in a first stage chemical reduction:Peroxide+Bisulfite→Water+Acid+Na++SO42−H2O2+NaHSO3→H2O+H++Na++SO42−
Then, to Neutralize the Resulting Acid:Acid+Caustic→Water+Na+H++NaOH→H2O+Na+
However, such a process, among other disadvantages, is labor intensive in nature, incorporate the uses of large quantities of expensive and hazardous chemicals, and results in concentrated salts (e.g., sodium, sulfate) being present in the waste stream, which is a significant contributor to total dissolved solids (TDS) and toxicity.